Horizontal injection molding machines comprise a mold clamping unit and an injection unit that are arranged in the horizontal direction on a base, and is constructed in the following manner, as shown in FIG. 30A, for example.
A mold clamping unit 96 is composed of a stationary platen 3, moving platen 4, rear platen 5, mold clamping mechanism TG, etc. The stationary platen 3 is fixed to a base BS, and is coupled to the rear platen 5 by means of tie bars 2. The moving platen 4 is located between the stationary platen 3 and the rear platen 5, and the tie bars 2 are passed individually through holes that are formed in the moving platen 4. The mold clamping mechanism TG is located between the rear platen 5 and the moving platen 4, and a crosshead 10 moves straight toward the stationary platen 3, thereby carrying out mold closing operation, as a ball screw BT rotates. Molds (stationary mold SM and moving mold MM) are fixed to the stationary platen 3 and the moving platen 4, respectively.
An injection unit 8 is provided on the side of the stationary platen 3 which is remoter from the moving platen 4. When it is moved toward the moving platen 4 by means of a ball screw & nut (nozzle-touch mechanism) NT, a nozzle 12 of an injection cylinder 11 projects through a through hole TH in the central portion of the stationary platen 3, and comes into contact with the stationary-side mold SM.
The injection molding machines described above require use of guide rods (not shown) for assisting the crosshead 10 in rectilinear movement. On the other hand, the injection unit 8 itself is mounted on the base BS of the injection molding machine by means of exclusive guide rods (not shown), such as linear motion guides, and is moved toward or away from the stationary platen 3. Thus, the guide rods for the crosshead 10 are arranged independently of the guide rods for the injection unit 8, in the mold clamping mechanism section.
Vertical injection molding machines comprises a mold clamping unit and an injection unit that are arranged in the vertical direction. Some of them have the same basic construction as the aforementioned horizontal injection molding machines. As shown in FIG. 30B, however, a vertical injection molding machine disclosed in Japanese Patent Publication, KOKAI No. 8-52756, has the following configuration. A moving platen 4 and a rear platen 5 are arranged above and below a stationary platen 3, respectively, that is fixed to a machine frame FR, and they are coupled by means of tie bars 2 that penetrate the stationary platen 3.
Molds (stationary mold SM and moving mold MM) are mounted on the stationary platen 3 and the moving platen 4. An injection unit 8 is located above the moving platen 4 (on the side remoter from the stationary platen 3), and is moved toward the moving platen 4 by means of a ball screw & nut (nozzle-touch mechanism) NT, whereupon a nozzle 12 of an injection cylinder 11 projects through a through hole TH in the central portion of the moving platen 4, and comes into contact with the moving-side mold MM. A mold clamping mechanism TG is located between the stationary platen 3 and the rear platen 5, and a crosshead 10 is moved straight toward the stationary platen 3 by means of a ball screw BT.
The aforementioned vertical injection molding machine, which uses a toggle-type mold clamping mechanism, also require use of guide rods (not shown) for assisting the crosshead 10 in rectilinear movement. On the other hand, the injection unit 8 is guided by exclusive guide rods (not shown) set up on the moving platen 4 as it moves toward or away from the stationary platen 3. Thus, the guide rods for the crosshead 10 are arranged, independently of the guide rods for the injection unit 8, in the mold clamping mechanism section.
Both the horizontal injection molding machine of FIG. 30A and the vertical injection molding machine of FIG. 30B are subject to the following problems.
(a) The overall length is equal to the sum of the length of the injection unit 8 and the length of the mold clamping unit 96, so that it is considerably long.
(b) The guide rods are needed to assist the crosshead 10 of the toggle-type mold clamping mechanism in rectilinear movement. Also, these guide rods are mounted in the mold clamping mechanism section. Since the guide rods for assisting the injection unit 96 in rectilinear movement are provided on the base BS of the injection molding machine or set up on the side of the moving platen 4 remoter from the mold clamping unit, however, the guide rods for the crosshead 10 cannot play the part of the guide rods for the injection unit 96.
An example that deals with the aforesaid problem (a) is disclosed in Japanese Patent Publication, KOKAI No. 8-57896. According to this prior art, the overall length of the injection molding machine is made shorter than the sum of the length of the injection unit 8 and the length of the mold clamping unit 96. Referring now to FIGS. 31A and 31B, this arrangement will be described.
FIG. 31A is a general view of a horizontal injection molding machine, in which a moving platen 4 and a rear platen 5 are arranged on one and the other sides, respectively, of a stationary platen 3 that is fixed to a machine frame FR, and the moving platen 4 and the rear platen 5 are coupled by means of tie bars 2 that penetrate the stationary platen 3.
Molds (stationary mold SM and moving mold MM) are fixed to the stationary platen 3 and the moving platen 4. An injection unit 8 is located on that side of the rear platen 5 remoter from the moving platen 4, and is moved straight toward the stationary platen 3 through a center hole 32 in the rear platen 5 by means of a ball screw & nut (nozzle-touch mechanism) NT. A nozzle 12 of an injection cylinder 11 projects through a through hole 33 in the central portion of the stationary platen 3, and comes into contact with the stationary-side mold SM.
As shown in FIG. 31B, a mold clamping mechanism TG is located between the rear platen 5 and the stationary platen 3, and a crosshead 10 (or a ball nut that replaces the crosshead) moves straight toward the stationary platen 3 as a ball screw BT rotates.
According to the prior art (FIG. 31A) disclosed in KOKAI No. 8-57896, as is evident from comparison between FIGS. 31A and 30A, the overall length of the injection molding machine is so short that the aforesaid problem (a) is solved. However, the aforesaid problem (b) is left unsolved. Thus, according to this prior art, the guide rods (not shown) are needed to assist the crosshead 10 (or the ball nut that replaces it). Since these guide rods cannot play the parts of any other members, however, a number of pieces of parts have to be provided.
According to this prior art, as shown in FIG. 31A, moreover, both the mold clamping mechanism TG and the injection cylinder 11 are located between the rear platen 5 and the stationary platen 3, so that the construction of the mold clamping mechanism TG is subject to restrictions.
This is because a plurality of links 88 must be arranged so as to surround the injection cylinder 11 in the center. In consequence, the ball screw BT, the crosshead 10 (or the ball nut that replaces it), and a coupling link for connecting each link 88 and the crosshead 10 must be provided for each of the links 88 so that the links 88 can bend and stretch separately, as shown in FIG. 31B. Also, there is a problem such that a strong bending moment acts on the ball screws BT that are in engagement with the crossheads 10 when the toggle links 88 are locked up.